Not sure how, but somehow I lost the ability to print to Microsoft Office Document Image Writer (MODI) delivered with Office 2003 under Vista - I was getting pretty ugly exceptions when trying and as ever needed to get it sorted 'cos I needed it quick!  The quickest way to resolve was to re-install MODI, which wasn't that painful:

• Close all running applications - if you have any Office application running, the driver will not be installed properly
• Go to the "Control Panel" and "Programs and Features"
• Click on"Microsoft Office 2003" and then click on "Change"
• Check "Add or Remove Features" and click "Next"
• On the bottom of the page check "Choose advanced customization of applications." and click "Next"
• Under Microsoft Office click on the + sign in front of "Office Tools"
• Locate "Microsoft Office Document Imaging", click the icon and select "Not Available"
• Click on "Update" - this will uninstall the broken MODI driver
• Repeat steps to get back to the point of expanding "Office Tools"
• Locate "Microsoft Office Document Imaging", click the icon and select "Run from My Computer"
• Click on "Update" - this will re-install the driver

Not sure how this got broken - I have installed a bunch of software since I last used it...